执行此操作的方法家族是：
int indexOf(String str)
indexOf(String str, int fromIndex)
int lastIndexOf(String str)
lastIndexOf(String str, int fromIndex)
返回指定子字符串的第一个（或最后一个）出现在此字符串内的索引[ 从指定索引处开始向前（或向后搜索）]。
String text = "0123hello9012hello8901hello7890";String word = "hello";System.out.println(text.indexOf(word)); // prints "4"System.out.println(text.lastIndexOf(word)); // prints "22"// find all occurrences forwardfor (int i = -1; (i = text.indexOf(word, i + 1)) != -1; i++) { System.out.println(i);} // prints "4", "13", "22"// find all occurrences backwardfor (int i = text.length(); (i = text.lastIndexOf(word, i - 1)) != -1; i++) { System.out.println(i);} // prints "22", "13", "4"
